indeterminate checkbox

- LS

Indeterminate checkboxes are displayed in a state which is distinct both from being checked or being unchecked. They are commonly used in hierarchical checkboxes to indicate that only some of the checkbox's descendants are checked.

IE

  1. 5.5
  2. 6 - 10
  3. 11

Edge

  1. 12 - 81
  2. 83

Firefox

  1. 2 - 3
  2. 3.5
  3. 3.6 - 75
  4. 76
  5. 77 - 78

Chrome

  1. 4 - 27
  2. 28 - 81
  3. 83
  4. 84 - 86

Safari

  1. 3.1 - 5.1
  2. 6 - 13
  3. 13.1
  4. TP

Opera

  1. 9 - 11.5
  2. 11.6 - 67
  3. 68

iOS Safari

  1. 3.2 - 12.1
  2. 12.2 - 13.3
  3. 13.4

Opera Mini

  1. all

Android Browser

  1. 2.1 - 4.3
  2. 4.4 - 4.4.4
  3. 81

Blackberry Browser

  1. 7
  2. 10

Opera Mobile

  1. 10 - 12.1
  2. 46

Chrome for Android

  1. 81

Firefox for Android

  1. 68

IE Mobile

  1. 10
  2. 11

UC Browser for Android

  1. 12.12

Samsung Internet

  1. 4 - 10.1
  2. 11.1

QQ Browser

  1. 10.4

Baidu Browser

  1. 7.12

KaiOS Browser

  1. 2.5

Indeterminacy does not affect a checkbox's checkedness state. It merely affects how the checkbox is displayed.

Resources:
iOS versions below 12 don't support indeterminate checkboxes (WebKit Bug 160484)
CSS-Tricks article